1. Field of the Invention
The present invention concerns the production of a woven reinforcement with multiple noncleaving layers much thicker in relation to known reinforcements of this type.
2. Discussion of Background Information
French patent application No. 87 02012 by the present assignee, which is the priority application of U.S. Pat. No. 4,848,414, describes a type of woven reinforcement with multiple noncleaving layers, and a highly resistant, e.g. very strong textile fiber base, such as glass, silica, carbon, "Kevlar", ceramic or other fibers, intended to form the reinforcements of composite materials.
This type of reinforcement is half way between reinforcement with a fibrous reinforcement piece in two directions (called 2 D) and reinforcement with a fibrous reinforcement piece in three directions (called 3 D). It is and conveniently known as a 2.5 D reinforcement, and is characterized by a structure equivalent to a noncleaving stacking of 2 D reinforcements, because the yarns of one direction, for example the warp yarns imprison the yarns, of the other direction (the weft yarns) of two adjacent layers. The term "layer" in this instance is defined by the number of superimposed parallel planes composed of the weft yarns.
As used herein the word reinforcement refers to a 2.5 D or 3 D type structure in which certain yarns, such as warp yarns, of one direction, imprison other yarns, namely the weft yarns, of the other direction of at least two layers. The number of layers is defined by the number of superimposed parallel planes composed of the weft yarns.
Thus, a noncleaving material is embodied with interlaced layers whose thickness depends on the number of layers and defined by an odd number, for example 5, 7, 9, 11, etc.
This type of woven reinforcement is produced on conventional units for weaving technical fabrics. The units include a positive dobby whose functioning is well-known. The aim of this device, by means of vertically mobile heddle frames and formed of frames bearing heddles into which the warp yarns are threaded, is to lift up or lower the warp yarns to allow for passage of the weft yarns. The warp yarns are available with the aid of a calibrating comb intended to maintain a certain warp width and regularly distribute the warp yarns over this width.
The greater the number of layers of the reinforcement, the greater the number of yarns for a given warp width. This implies increasing the number of yarns per tooth of the calibrator.
Given the fact that each yarn needs to pass into the eye of a heddle of one of the heddle frames of the dobby, the dobbies currently commercially available do not have a sufficient capacity, in terms of the number of heddle frames, to ensure a correct distribution of all the yarns. Accordingly for a number of layers equal to or greater than nine, it is impossible to make this type of reinforcement, because the yarns of a given tooth of the calibrator risk being caught up during the movements of the heddle, frames of the dobby.